1. Field of the Invention
The present invention relates to an infusion pump system of the type comprising an electrical motor and a pump, for continuously injecting a medicinal substance contained in a supply chamber into a catheter connected to a patient's body, thanks to an infusion tube connected to the pump, said pump comprising flattening means driven by the motor for flattening a portion of the infusion tube so as to exert a pressure and inject the medicinal substance into the catheter.
2. Description of Prior Art
More and more human diseases are treated by injecting a medicinal substance into the patient's body. As an example, in the treatment for diabetes, it is necessary to perform at regular time intervals insulin injections to the patient. Other diseases like cancer are also treated thru injecting of medicinal substances. But frequent injections using needle and syringe are a problem with respect to the regularity of the injections to be performed, and even more, the skin damages incurred after multiple performed injections.
The solution has then been for the patient to follow a continuous treatment thanks to an infusion needle fixed at the input of the catheter connected to the patient, in general with an implanted chamber, connected to a pump.
The improvement brought about by this technique has been that the patient carries the pump along, in a pocket, or hanging from a belt. The pump driven by a small electrical motor, continuously injects the medicinal substance in the catheter and thus provides the necessary chimiotherapy, without having to always perform continuous injections thru needle and syringe.
There is currently available on the market several pump types aimed at continuous infusion of medicinal substance. The first type comprises pumps having rollers. In those pumps, rollers are generally placed at the periphery of a cylinder rotated by the electrical motor. The rollers in turn flatten a portion of the infusion tube. The system is so arranged that two or more rollers are simultaneously in contact with the infusion tube. Thus a first roller flattens the infusion tube more and more and prevents any flow within, while at the same time a second roller downstream, frees the portion of the tube previously flattened and thus induces a flow in the infusion tube, due to the pressure exerted by the flattening with the first roller. One can refer to documents EP-19816, EP-19817 and EP-197179 which deal with that same type of pump.
Pumps with rollers, although very simple, have the drawback of featuring rotating elements for exerting the flattening on the infusion tube. Inevitably, frictions occur between the rollers and the infusion tube, which leads to internal constraints within the walls of the infusion tube and consequently a permanent deformation of said walls. Consequence of the walls deformation is that metering precision for the medicinal substance to inject is impacted. Thus pumps with rollers have an accuracy of about 10 to 15%. Such a low accuracy is not acceptable for substances requiring a high injection precision.
A second type of pumps is of the type with fingers. In such a pump, several fingers flatten the infusion tube in different places and intermittently. When at least one finger flattens the infusion tube in one place, thus blocking any upstream flow in the infusion tube, at least one other finger releases downstream from the pressure it exerted on the infusion tube, and therefore enables the downstream flow of the medicinal substance, started with the flattening finger.
Pumps with fingers do not have the drawback of frictions occurring with the infusion tube walls since there is no rotating element moving along the infusion tube. Those pumps are therefore more precise than the pumps with rollers. An accuracy higher than 5% can be reached with pumps with fingers. Unfortunately the latter pumps require a mechanical driving of the fingers involving a rather complex system of cams. To still increase the accuracy of this type of pump, the number of fingers has been increased, along with the complexity of the implementing mechanics. Thus the pump described in document U.S. Pat. No. 4,671,792 has seven fingers. The complexity renders it impossible to realize a miniaturized pump with fingers. Another drawback, not the least of them, is that the complexity of the fingers driving system is accompanied with a high power consumption and thus a frequent replacing of the electrical motor batteries.
A third type of pump being also used for infusions is described in patents U.S. Pat. No. 2,818,815 and EP-A-103.073. This type of pump features a rigid part under the form of a disc coupled to the driving shaft of the pump motor and having an axis at a certain angle with said shaft, also called nutation angle. When the motor rotates, it drives the disc in an oscillatory motion such that the external rim of the disc flattens the infusion tube placed as a ring in a plan perpendicular to the motor driving shaft.
Pumps of the type above partly solve the above-mentioned drawbacks in that they do not have rotating elements such as the ones in pumps with rollers, or complex elements such as the ones required in the pumps with fingers. However, although it is mentioned in the above-referenced documents that the disc moved in an oscillatory motion does not rotate, nothing in there prevents it from rotating and thus exerting a friction on the infusion tube at the same time it flattens it. Besides, pumps as described in the prior art do not allow an accurate control of the injected substance flow.